Some conventional position detecting device uses a resolver, an amplifier circuit and a microcomputer as disclosed in US 2003/0111974 A1 (JP 2003-166803 A). The sine phase signal and the cosine phase signal produced by the resolver are amplified by the amplifier circuit in the interface circuit and applied to the microcomputer. The microcomputer calculates a difference between gains of the amplified sine phase signal and the amplified cosine phase signal produced by the I/F circuit, and corrects the outputs of the amplifier circuit in accordance with the calculated difference. Thus, the difference in the detected angle caused by the difference of the gains in the outputs of the amplifier circuit is reduced.
If the sine phase signal and the cosine phase signal are amplified, the positive amplitude and the negative amplitude of each of the amplified sine phase signal and the amplified cosine phase signal sometimes vary from each other. Therefore, the amplified sine phase signal and the amplified cosine phase signal are corrected based on the difference of gains of the sine phase signal and the cosine phase signal.
However, the difference between the positive amplitude and the negative amplitude of the sine phase signal or the cosine phase signal is not considered. As a result, it is not possible to reduce any error in the detection of the angular position caused by any difference between the positive amplitude and the negative amplitude of the amplified sine phase signal or the amplified cosine phase signal.